NO. 3 LANGLEY MEMOIB ON MECHANICAL PLIGHT 69 



less than 7 kilogrammes. From 60 to 90 pounds of steam could be maintained 

 by the boilers for about 2 minutes, at which pressure the engines developed about, 

 0.66 brake horse-power, driving the 70 cm., 1.25 pitch-ratio propellers at 700 K. 

 P. M., and giving a lift of from 2.6 to 3.0 kilos (5.7 to 6.6 pounds), or about 40 

 per cent of the flying weight. 



The wings and tail had a total surface of 2.62 sq. m. (28.2 sq. ft.), giving a 

 ratio of 2.7 kilos to 1 sq. m. of wing surface (1.8 sq. ft. per pound). If the hull 

 resistance be neglected, the soaring speed of this aerodrome was about 5.9 metres 

 (19 feet) per second, or 13 miles per hour. 



Turning now to the completed No. 5, its frame was of the " double mid- 

 rod " type described above, the two tubes which formed the frame being pro- 

 longed at the front and rear to afford points of attachment for the wings and 

 tail. The range through which the wings could be shifted to adjust the position 

 of the center of pressure was, however, very small. The hull, which, it will be 

 remembered, contained all the power generating apparatus, was much stronger 

 and heavier than that of No. 4, and resembled somewhat the hull of a ship. It 

 had a frame-work of steel tubing brazed to the midrod, to which an outer 

 sheathing of sheet aluminum 0.3 mm. thick was attached. It was, however, ex- 

 cessively heavy, weighing nearly 800 grammes. 



The engine, which was mounted near the front of the hull, was the single 

 cylinder, one horse-power engine, described above, which drove the two propel- 

 lers by suitable gearing. The remaining parts of the power plant were identical 

 with those already described in connection with No. 4, but the more advantage- 

 ous location of them in No. 5 rendered them somewhat more efficient. 



It had been planned to use 80 cm. propellers of 1.25 pitch-ratio on No. 5, but 

 it was found in the shop tests of the aerodrome that the cross-frame was not 

 strong enough to withstand the strains, and that the engine could be made to 

 work much more steadily with a smaller propeller. Accordingly, propellers of 

 70 cm. diameter and 1.25 pitch-ratio, similar to those used on No. 4, were finally 

 substituted. 



For floating the aerodrome, when it descended into the water, an air-cham- 

 ber similar to that of No. 4, but of a larger capacity was provided. With this in 

 place on the aerodrome, it was calculated that, if all the pails except this float 

 and the gasoline tank were filled with water, there would still be a buoyancy of 

 over 2 kilogrammes. 



The total weight of No. 5 was 8200 grammes, or with its full supply of fuel 

 and water 9200 grammes. In this aerodrome the same boilers used in No. 4 

 were capable of maintaining for at least a minute 115 pounds of steam, so that 

 the engine now gave the maximum of one brake horse-power for which it was 

 designed, and, driving the 70 cm. propellers, lifted repeatedly nearly 45 per cent 

 of the flying weight. 



